1. Field of the Invention
The present invention relates to an image projection device capable of super-imposing an on-screen information display onto the main image being projected. In particular, the invention provides for an image projecting apparatus including an on-screen displaying circuit capable of adjusting a location of a superimposed image in response to varying aspect ratios of the main image being projected.
2. Description of the Related Art
A liquid crystal projector has lately attracted considerable attention. To obtain a large-sized image, a halogen lamp or the like emits light from the rear of a liquid crystal panel. Thereby, an image on the liquid crystal display is enlarged and projected onto a front screen through a projection lens. The advantages this structure is that the liquid crystal display is small and light, yet the size of a picture image can be easily enlarged by the scale factor of the projection lens. Therefore, a television apparatus capable of obtaining a large-sized picture image from a small and light weight device can be developed.
Since the liquid crystal projector is a kind of television receiver, a receiving circuit has been developed which is capable of displaying additional information such as a channel display, an image menu display and a picture in picture display.
FIG. 10 is a block diagram showing an on-screen displaying circuit in, use. The circuit illustrates a circuit formation which determines a display position of an on-screen signal in the vertical direction when the on-screen signal is displayed on a television picture plane. In FIG. 10, a counter 31 is operated by inputting a horizontal synchronizing signal HD into a display position circuit as a clock pulse, and using a vertical synchronizing signal VD as a reset pulse, a display position timing pulse is produced which corresponds to a display position of the on-screen signal. Input ends d and e of a switch 32 are selectively changed over using this display position timing pulse, so that an output video signal in which an on-screen signal is superimposed will be obtained and supplied to a displaying device 33 composed of a liquid crystal panel and a cathode ray tube. The image on which the on-screen information is superimposed is displayed by the displaying device 33. In a projecting-type television receiver, the image displayed on the displaying device 33 is further enlarged and projected on a screen 35 through a projection lens 34.
FIG. 11 shows a timing of a signal for each portion of FIG. 10. In FIG. 11, (a) and (b) represent a horizontal synchronizing signal HD and a vertical synchronizing signal VD supplied to the counter 31, respectively. Also, (c) represents counter output (that is, a display position timing pulse) which is output when a predetermined number (the number of n) of the horizontal synchronizing signals HD are counted after the counter 31 is reset by a trailing edge of the vertical synchronizing signal VD. (d) and (e) represent a video signal and an on-screen signal supplied to two input ends d and e of the switch 32, respectively. A video signal on which an on-screen signal is selectively superimposed, as shown in (f), is output from the switch 32.
In our highly oriented information age, it has been desired to increase the aspect ratio of video software from 16:9, as represented Hi-Vision broadcast size, a Cinema Scope size or a vista size, to an aspect ratio of 16:12 (=4:3). In current video software, for example as shown in FIGS. 12(a) and 12(b), if a zoom ratio of a projection lens of a liquid crystal projector is changed, an image having the ratio 16:9 can be projected to fill the screen 35. FIG. 12(a) represents a case in which a liquid crystal picture image having the ratio 16:12 is enlarged and displayed on the screen 35, also having the ratio 16:12. FIG. 12(b) represents a case in which a picture image having the ratio 16:9, such as a Hi-Vision broadcast, is displayed on the liquid crystal picture plane having the aspect ratio 16:12 and enlarged and displayed on the screen 35 having the ratio 16:9.
In this case, as shown in the timing chart of FIG. 11; a display position of an on-screen signal is determined regardless of the contents of a video software. Therefore, as shown in FIG. 13(a), there is no problem in the case when an on-screen display is superimposed onto the liquid crystal picture image having the aspect ratio 16:12 and enlarged and displayed on the screen 35 having the same aspect ratio 16:12. However, as shown in FIG. 13(b), a part of the superimposed on-screen display will be projected off of the projection screen 35 when a picture image having the aspect ratio 16:9 is displayed on the liquid crystal picture plane having the aspect ratio 16:12 and enlarged and displayed on the screen 35 having the aspect ratio 16:9. As a result, not all of the superimposed on-screen information will be displayed proper.
The size of a picture image can be easily changed by a zoom ratio of a projection lens in a projecting-type image displaying apparatus, such as a liquid crystal projector. However, it is inconvenient that a superimposed on-screen display goes beyond a projection screen as the size of a picture image is determined in accordance with the video software.